This post has been updated.

There was a telling moment in President Trump’s fateful call this summer with Ukrainian President Volodymyr Zelensky, when Trump said, “The former ambassador from the United States, the woman, was bad news.” Trump didn’t even know Marie Yovanovitch’s name; all he knew was that Rudy Giuliani wanted her gone, so he recalled her from her post.

Trump probably knows Yovanovitch’s name now. She’s one of a parade of government officials testifying before the impeachment inquiry, officials who simply by telling the truth might doom Trump to be a one-term president even if he survives impeachment. So the best way to understand how Trump is besieged might be by looking at the different kinds of people who have either had enough of him or are being forced by subpoena to share what they’ve seen.

The nonpartisan professionals. While every president gets to appoint a few thousand officials (often called political appointees), they also inherit many times that number of civil servants, people who stay through Republican and Democratic administrations performing all the tasks of government. Some of these are so distant from the Oval Office that Trump probably doesn’t even know they exist (a crop yield analyst at the Department of Agriculture, say) but some of them are much closer to him, even working in the White House.

It’s these professionals who have been the most appalled at what they have seen Trump do. The most important of them is the whistleblower who sounded the alarm on the Ukraine scandal. Yovanovitch is another; she apparently lost her job because her efforts to help Ukraine overcome corruption drew the ire of Giuliani and his associates, who were seeking to make the country more corrupt so they could cash in.

William Taylor, who has been running U.S. diplomacy in Ukraine since Yovanovitch’s departure, is another career government official who has done immense damage to Trump. “As I said on the phone, I think it’s crazy to withhold security assistance for help with a political campaign,” Taylor said in a text that has now become key evidence in establishing the quid pro quo Trump set for Ukraine.

There are other career professionals whose names we’re now learning, since they will likely be called to testify. Michael McKinley, who recently resigned as a top adviser to Secretary of State Mike Pompeo. George Kent, the State Department official in charge of Ukraine, who testified Tuesday. And there might be more to come.

The Republican professionals. These are people who served in previous Republican administrations, but unlike your typical Trump crony brought some actual expertise to their jobs. Kurt Volker, who was acting as a coordinator for Ukraine policy and apparently helped Giuliani’s suspect efforts in the country, falls into this category. So does Fiona Hill, who served as Trump’s top adviser on Russia; Monday she offered what sounds like devastating testimony on the rogue foreign policy operation Giuliani was operating at Trump’s direction.

Another key figure is former national security adviser John Bolton, who reportedly told Hill, “Giuliani’s a hand grenade who’s going to blow everybody up,” and advised her to bring her concerns to the National Security Council’s chief legal adviser. If Bolton were to turn on Trump, it could be the most dramatic development of this scandal.

The semi-Trumpite Republicans. These are people who are (or were) on board with Trump’s agenda, but might not stick by the president when their own necks are on the line. Most prominent among them is Gordon Sondland, who bought himself a position as ambassador to the European Union with a $1 million donation to Trump’s inaugural. Sondland seems to have been acting as an enabler of Giuliani’s schemes in Ukraine, but might do some interesting bean-spilling later this week.

For those in any of these categories, “turning on Trump” might consist of nothing more than telling the truth under oath. And for the Republicans among them, we should note that doing so is hardly a good career move. If you’re a Republican in this administration — no matter what you think of the Ukraine debacle — the safest thing to do is probably to keep your head down and stay loyal.

Because the entire Republican Party is implicated in the horror of the Trump presidency, the kind of true reckoning those who decided to go work for him would deserve in a more just world will not happen. Too many people are complicit. Today’s Trump enabler will be tomorrow’s think tank senior fellow or well-remunerated corporate consultant, with jobs in future Republican administrations theirs for the taking.

Nevertheless, for all the grifters and ideological extremists Trump has installed in his administration, there was also a kind of personnel time bomb waiting to go off. It’s made up of both civil servants and political appointees, people throughout his administration who were not quite the kind of rabid true believers we see defending Trump on TV. For nearly three years, they’ve done their jobs and hoped everything would turn out for the best.

But in the right circumstances, they’ll either decide to jump ship or simply have no choice but to tell what they know. It’s already happening, and there’s nothing Trump can do to stop it.

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